The present invention concerns in general terms a method and device for determining the distribution of a product present in a reservoir. The type of product and reservoir considered here are such that the product is liable to be distributed heterogeneously in the reservoir, meaning that different zones of the reservoir can contain different quantities of product.
The invention relates more especially to a method and device for determining the distribution of ink in a reservoir of an image transfer device.
The type of reservoir containing a porous body soaked with ink in liquid form is widely used amongst image transfer devices, such as printers or facsimile machines. However, this type of reservoir can present the following problem. As a result for example of poor storage conditions, or a long period of time between two utilisations of the image transfer device, the ink contained in the porous body of the reservoir may be distributed heterogeneously in the reservoir. The functioning of the image transfer device is then impaired; for example, if there is less ink near to the ink outlet orifice than in the rest of the reservoir, the user will have the impression that the reservoir is empty. A reservoir containing ink in powder form, for a laser printer, can present a similar problem.
For image transfer devices which use ink jet technology, such as ink jet printers, devices and methods have been designed for determining the quantity of ink remaining in the reservoir.
A first type of known detection uses the electrical characteristics of the ink by measuring the resistance of the latter between two electrodes.
The document EP-A-0 370 765 describes a device for detecting the quantity of ink present in a reservoir, comprising two electrodes placed in the duct connecting an ink ejection head to the ink reservoir as well as a means for detecting the electrical resistance between the two electrodes. The first electrode is situated close to the ejection head while the second is distanced from the latter. A potential difference is applied between these two electrodes. The resistance of the ink is measured. Thus, in the event of a notable decrease in the expected ink flow, the resistance value increases, which enables this decrease to be detected.
The use of this device does not enable the distribution of ink in a reservoir to be measured.
A second known type of detection uses the electrical characteristics of the ink by measuring the capacitance of the latter.
The document U.S. Pat. No. 4,700,754 describes the detection of the level of liquid ink in a flexible reservoir which contracts as the level of ink decreases. The bottom external wall is coated with a conducting layer forming one electrode of a capacitor. The reservoir wall acts as a dielectric for the capacitor thus formed whilst the ink surface in contact with the bottom wall forms the second face of the capacitor. A measuring electrode placed in the centre of the reservoir connects the ink to a measuring device. When the quantity of ink decreases, the ink surface against the conducting layer coating the wall decreases, and therefore the equivalent capacitance value also decreases.
This second type of detection is used for a cartridge with flexible walls and cannot be applied to rigid cartridges. This is because the contact between the measuring circuit and the ink can be made only if the top wall, when crushed, forces the measuring electrode to be in contact with the ink.
Moreover, this measurement of the ink level is possible only for liquid ink contained in a reservoir without a porous body. The distribution of ink cannot be measured with this known device.
The present invention aims to remedy the drawbacks of the prior art by providing a device and method for determining the distribution of a product contained in a reservoir.
The invention starts from the observation made by the inventors in the course of tests, that an electrical excitation of a product causes electromagnetic radiation from the latter, and that this radiation depends not only on the excitation signal, but also on the quantity of product surrounding the electrode.
In general terms, the invention proposes a method for determining the distribution of a product present in a reservoir, characterised in that it comprises the operations of:
exciting a plurality of points in the reservoir, and
processing the radiation caused by the excitation operation.
Correlatively, the invention proposes a device for determining the distribution of a product present in a reservoir, characterised in that it comprises:
an excitation means adapted to excite a plurality of points in the reservoir, and
a means for processing the radiation caused by the excitation means.
The method and device according to the invention have not only the advantage of solving the technical problem stated above, but also of being adaptable to a large number of existing image transfer devices.
Generally, the invention is applicable to any product, notably a product forming a consumable product used in a given device.
Preferably, the invention applies to ink contained in the reservoir of an image transfer device. xe2x80x9cInkxe2x80x9d here means any liquid, gaseous, solid or powder product designed to modify an optical or physical factor of the printing medium.
According to a preferred embodiment, the method is characterised in that on the one hand a plurality of electrodes is distributed inside the reservoir, and on the other hand it comprises the operations of:
supplying the said electrodes with a predetermined excitation signal,
picking up electromagnetic signals caused by the supplying of the electrodes with the excitation signal, in order to produce electrical signals representing the electromagnetic signals, and
processing the electrical signals to produce a signal representing the distribution of product present in the reservoir.
Correlatively, in the preferred embodiment, the device is characterised in that it includes:
a plurality of electrodes disposed in the reservoir, so as to be in contact with the product,
a means for supplying the electrodes with a predetermined excitation signal causing electromagnetic signals radiated by the product,
a means for sensing the electromagnetic signals caused by the respective supplying of the electrodes and producing electrical signals representing the electromagnetic signals, and
a means for processing the electrical signals into a signal representing the distribution of product present in the reservoir.
It will be observed that these arrangements are particularly simple to implement as regards both the structure of the reservoir and the electronic processing means.
In the preferred embodiment, the supplying and sensing operations of the method are carried out successively for each of the electrodes, with the same excitation signal, or, as a variant, the supplying operation comprises the simultaneous supplying of the electrodes with excitation signals different from each other.
According to a first preferred embodiment which is simple and economical to implement, the processing operation includes the operations of:
detecting the respective amplitude of the electrical signals,
calculating the differences between one of the amplitudes and the other amplitudes, and
producing the signal representing the distribution of the product from a value given in a calibration table as a function of the differences calculated.
Correlatively, the processing means includes an envelope detector for detecting the amplitudes of the electrical signals, a means for calculating the differences between one of the detected amplitudes and the other detected amplitudes and a means of converting the calculated differences into a distribution of the product present in the reservoir.
According to a second preferred embodiment, less sensitive to any external perturbations than the previous one, the processing operation includes the operations of:
detecting a respective phase difference between each of the electrical signals and the excitation signal,
calculating the differences between one of the phase differences and the other phase differences, and
producing the signal representing the distribution of the product from a value given in a calibration table depending on the calculated differences.
Correlatively, the processing means includes a phase comparator for determining the phase differences between the excitation signal and each of the electrical signals respectively, a means for calculating the differences between one of the phase differences and the other phase differences and a means for converting the calculated differences into a distribution of the product present in the reservoir.
According to a variant of the second embodiment, the processing operation includes:
the detection of the phase differences between the electrical signals considered in pairs, and
the production of the signal representing the distribution of the product from a given value in a calibration table according to the detected differences.
Advantageously, the method also includes the operation of displaying a representation of the distribution of product present in the reservoir, and the device therefore has a display means. By virtue of this display, the user always knows the distribution of product. The method can also include the operation of transmitting the signal representing the distribution of product present in the reservoir to a remote device in order that it may display a representation of the distribution of product present in the reservoir.
Advantageously, the electrodes are situated in different parts of the reservoir, and in particular a first electrode is situated near to an outlet orifice of the reservoir and at least one second electrode is situated at a distance from the first. In this way, the detection conditions are optimised.
According to preferred characteristics of the invention, allowing simple and economic implementation thereof, the means for supplying the electrodes includes an oscillator connected to the electrodes via a switch, and a selector for selectively supplying one of the electrodes.
Advantageously, the excitation signal is an alternating high-frequency signal, preferably at a frequency above 10 MHz. Such an excitation signal produces radiated electromagnetic signals which are easily detectable and easy to use within the framework of the invention.
According to one embodiment, the means for supplying the electrodes provides a signal of different frequency to each of the electrodes. In this case, the device has filters for filtering the electrical signals and supplying the filtered signals to the processing means.
Preferably, the means for sensing the electromagnetic signal is a metal component forming an antenna, such as a metal ribbon.
The invention is adaptable to determining the distributions of product present in several reservoirs respectively; the device is then characterised in that it includes:
a plurality of electrodes disposed in each reservoir, so as to be in contact with the product present therein,
a means for supplying the electrodes of each reservoir with a predetermined excitation signal causing electromagnetic signals from the product in each reservoir,
a means for sensing the electromagnetic signals and for producing electrical signals representing the electromagnetic signals, and
a means for processing the electrical signals into a signal representing the distribution of product present in each reservoir.
In another aspect, the invention concerns a product reservoir, such as an ink reservoir, characterised in that it includes a plurality of electrodes disposed in the reservoir, so as to be in contact with the product, and connecting means enabling supplying with an excitation signal causing electromagnetic signals radiated by the product.
In yet another aspect, the invention concerns an image transfer device comprising a reservoir containing ink, characterised in that it includes:
a plurality of electrodes disposed in the reservoir, so as to be in contact with the ink,
a means for supplying the electrodes with a predetermined excitation signal causing electromagnetic signals radiated by the ink,
a means for sensing the electromagnetic signals caused by the supplying of the electrodes and for producing electrical signals representing the electromagnetic signals, and
a means for processing the electrical signals into a signal representing the distribution of ink present in the reservoir.